Ethernet switches are used to provide end users of network connectivity to the data network. Switches have a number of network ports which may be categorized as uplinks and downlinks of data connection. An uplink port is one used to connect a switch to an upstream distribution switch, and a downlink port is a port on the switch used to connect to an end user terminal such as a PC.
Network administrators build a larger network by connecting edge switches to core distribution switches through high bandwidth uplinks. Often two or more uplinks are connected to the same or different distribution switches to achieve the uplink data backup. In this manner, if one of the uplink fails, the edge switch still remains connected to the core data network through one of the other uplinks. In such uplink configuration, only one of the uplinks may be configured to be forwarding data at a given time to avoid data forwarding loops.
Topology changes within the network can result in flushing of MAC address tables by spanning-tree. In turn, flushing of MAC addresses result in flooding of frames by the networking devices until the MAC addresses are learned. In general, network administrators strive to reduce the flooding caused due to topology changes.